In vitro flow properties of glaucoma implant devices

PURPOSE: To develop a protocol for testing glaucoma implant devices and to use this protocol to characterize devices currently available. METHODS: The following devices were obtained: Ahmed Glaucoma Valve Implant, Baerveldt Implant, Krupin Eye Valve, Joseph Valve, and OptiMed Glaucoma Pressure Regulator. Pressure per unit time was measured in real-time during ramped pressure perfusion of the implant devices with an open-manometer system. Each device was measured during a 10 minute interval while a constant flow of fluid was pumped into the system. The open manometer allowed the resistance of the devices to generate a pressure head which was monitored by computer. Four independent runs were averaged for each device. RESULTS: The Ahmed devices demonstrated reliable valve performance with a mean opening pressure of 13.65 mm Hg, a facility flow of 1.2 μL/min/mm Hg and a closing pressure of 6.1 mm Hg. The Baerveldt devices had a mean facility flow of 7.56 μL/min/mm Hg. The Joseph devices had the most variable performance, opening from 2.05 to 6.21 mm Hg. Two of 4 Joseph devices had high facility of flow (5 μL/min/mm Hg). The Krupin devices had a mean opening pressure of 6.25 mm Hg in 3 of 4 devices. The remaining Krupin device did not exhibit valve behavior. The OptiMed device did nor reveal an opening pressure, and had a mean facility of flow of 7.08 μL/min/mm Hg for high flow and 6.20 μL/min/mm Hg for low flow. CONCLUSION: An objective test protocol for glaucoma implant devices was demonstrated. All implant devices had high facility of flow compared to the normal eye and can be grouped into very high facility (Baerveldt and OptiMed), and high facility (Ahmed, Joseph and Krupin). Only the Ahmed device had consistent valve behavior. None of the devices created enough resistance to explain long-term clinical failure of glaucoma drainage device surgery.